The Toronto Salmon Run

Guest Post by Sara Bowman, currently enrolled in the Professional Masters of Environmental Science program at the University of Toronto-Scarborough

The Toronto Salmon Run

Toronto has been called a lot of things, but I think my favourite is “A City Within a Park”. Between High Park, the Rouge, and countless other parks based around our river systems, there are so many opportunities for people to connect with nature and forget they live in a city that is 2.6 million people strong. Despite my frequent excursions into the parks of Toronto, I still will often see something new that spurs a whole whack of questions and excitement about the area I call home.

Case in point: the salmon run! Cycling to work on October 13th I was lucky enough to witness my very first salmon run along the Don River, between Sheppard and Finch. You couldn’t help but notice the nearly 2 foot long fish struggling northward against the current, especially when a few individuals would have a violent encounter followed by swimming speedily away. I whipped out my cell phone and took as many videos and pictures as I could without being late to work. All throughout my shift questions started cycling through my head. Where in the river do the fish spawn? How many types of salmon are in Lake Ontario? Where did they come from? How are they faring from a conservation perspective? In no particular order, here are some answers I found to these questions!

Photo Credit: Tony Bock, The Toronto Star

First of all – I think my salmons were Chinook, which is the largest of the Pacific Salmons[1]. Chinook Salmon were intentionally introduced to Lake Ontario some time in the 1960s (Coho Salmon, another Pacific Salmon species, was introduced at around the same time), mainly for sport fishing, and as a bio-control for non-native fishes[1]. Their introduction was also important for essentially replacing the native Atlantic Salmon and Lake Trout, which were the top predators[1]. Atlantic Salmon were extirpated from Lake Ontario in the late 1800s due to fishing pressures, and today programs like Bring Back The Salmon are undertaking re-introduction efforts, and also habitat restoration and public outreach so that extirpation doesn’t just happen again[2].

Although thousands of individuals of Chinook are stocked in Lake Ontario every year, it is believed that natural reproduction occurs, and that they are well on their way to becoming naturalized[1]. In an ocean system, Chinook Salmon migrates up streams (the ones where they were born) from the Pacific Ocean to mate and lay eggs (spawn). Once they have spawned, they die, unlike the Atlantic Salmon which makes the trip back down to the Ocean after spawning[3]. The adult female will choose a site to make her “redd” (essentially a nest for the fish eggs) based on the water velocity and depth, and on the composition of the substrate, which should be gravel[3]. At first I was confused about how the fish managed to get so large in just a year, but it turns out that once they hatch after 3-5 months, they can spend up to 2 years in the streams where they undergo certain changes to prepare them for salt-water life[3]. Once they are back in the Pacific, they will stay there to feed and grow for up to six years[3]!

Lake Ontario is home to seven species of fish in the family Salmonidae, of which only 3 are native: the Atlantic Salmon, the Lake Trout, and the Brook Trout[1]. The Brown Trout, Chinook Salmon, Rainbow Trout, and Coho Salmon were all introduced[1].  My first thought, and this may be yours to, is how Atlantic Salmon could be considered native to Lake Ontario – after all “Atlantic” is in their name, and the distance between the Atlantic and Lake Ontario is pretty far, even for a determined migrating fish. So how did the fish get into our lakes? The Ice Age. The last one ended about 12,000 years ago, and Toronto was under about a kilometer or two of ice. When the glaciers retreated northward, basins were carved into the land and were filled with the melted water, and because of all the extra water from the ice, the St. Lawrence connection between the lake and the ocean was stronger[4]. Because the Atlantic Salmon had some freshwater adaptations for when it was spawning, it was able to naturalize to its new all freshwater environment[1].

National Oceanic and Atmospheric Association, 1999 

As the 2012 Fishes of Toronto report explains, as settlement around Lake Ontario and its streams increased in the 1800s and 1900s, the river temperatures increased, erosion increased, pollution from sewage increased, and physical structures blocking migration like dams were built. This would ultimately result in the local demise of the species from Lake Ontario.  Luckily, as I mentioned above, restoration efforts are under way to restore Atlantic Salmon populations. I wondered whether or not here might be some detrimental effects on any of the salmonid populations when or if Atlantic Salmon makes a come back, but a study in Ecology of Freshwater Fish from 2012 by Jessica Van Zwol and others found that a mix of Atlantic Salmon, Brown Trout and Rainbow Trout in stream breeding grounds did not significantly impact productivity[5]. Lake Trout is another native of Lake Ontario that suffered major population declines. In the 1970s some restoration efforts were began, but today the population has to be maintained by fish reared in a hatchery – the amount of natural reproduction occurring is not enough to prevent the species from extirpation[2].  

What can we do to ensure the future of these top open-water predators in Lake Ontario? For starters, we can be more conscious of what we are putting down our drains – it leads to the rivers and can pollute them. Be aware of proper chemical disposal. You can engage in tree planting programs along riverbanks to help prevent erosion. You can even help with salmon hatchery programs and habitat restoration to help give the populations a boost so that they can maintain their ecological roles, and be around for fishers to fish for generations to come.

Thanks for reading!!

References

1.Fishes of Toronto: A Guide to Their Remarkable World. City of Toronto, 2012. URL: 
https://www1.toronto.ca/City Of Toronto/Toronto Water/Files/pdf/F/Fishes of TO_PRINT_Feb23%5B1%5D.pdf
2. Lake Ontario Atlantic Salmon Restoration Program. Bring Back the Salmon Lake Ontario. 2013. URL:  http://www.bringbackthesalmon.ca/?page_id=12 
3. Chinook Salmon. NOAA Fisheries. Updated May 14, 2015. URL: http://www.nmfs.noaa.gov/pr/species/fish/chinook-salmon.html 
4. About Our Great Lakes: Background. National Oceanic and Atmospheric Administration. 
[U.S. Army Corps of Engineers and the Great Lakes Commission] Published 1999. URL: 
http://www.glerl.noaa.gov/pr/ourlakes/background.html 
5. Van Zwol, J., Neff, B., Wilson, C. 2012. The effect of competition among three salmonids on dominance and growth during the juvenile life stage. Ecology of Freshwater Fish. 21: 533-540. Accessed online: http://publish.uwo.ca/~bneff/papers/Van Zwol et al_Salmonid Dominance.pdf

#ibs2015 – Confronting uncertainty, biases and the unknown

The 2015 meeting of the International Biogeography Society just came to an end, and even for someone who wouldn’t traditionally consider themselves a ‘biogeographer’ there were many interesting topics and talks to see.

The focus of most talks was on biological patterns over space and/or time (or ‘deep time’, which is a fun phrase to throw around), and the talks emphasized how sophisticated statistical methodologies for such questions have become. The extent and complexity of approaches for making inferences from limited existing information, be it phylogenetic, distributional, or fossil and pollen records, is pretty amazing.

Such complicated inference needn't and shouldn't come at the cost of careful scientific work, and must include recognition of uncertainty and biases. The final sessions of the conference acted as an excellent (and at times provocative) reminder of this. For example, Joaquin Hortal advocated the development of ‘maps of ignorance’, which instead of showing the typical distributions of known information, highlight where information is missing and new sampling should be emphasized. Not only is information sometimes missing, but its value degrades over space and time. The value of a sample declines the further away you get from that site or the more different the spatial scale; samples over 50 years old may not represent current conditions any more. Predictions should consider or even incorporate this uncertainty.

Catherine Graham, David Nipperess, and Jon Chase all gave talks similarly emphasizing how fundamental consideration of scale and extent is. This is as true for phylogenetic community analysis (Graham, what extent or size of tree should be considered for analyses of community phylogenetics?); for rarefaction of phylogenetic diversity (Nipperess); or for measures of beta-diversity (Chase). Without this context, we are likely to be misunderstanding our results.

Finally, David Currie gave a damning critique of macroecology. Unfortunately, he said, macroecology seems to be a field where hypothesis testing is rare and conclusions are drawn based on spurious correlations with little explanatory and even less predictive ability. For example, why has the study of latitudinal gradients in richness progressed little beyond a list of possible correlates after more than 30 years of attention? Though Currie was focused on his own field, his comments were relevant to many ecological approaches. Currie expressed concerns about areas where scientific methods were being given short shift. In particular, he noted a lack of appropriate hypothesis testing and strong inference. Instead there is a tendency for studies to look for evidence in support of a hypothesis of interest, rather than attempting to falsify a hypothesis. Supporting evidence, sadly, does not actually increase the probability that a hypothesis is true, since the evidence could equally support some other, currently unconsidered, hypothesis. Further, correlations between variables of interest are at best a weak test of a hypothesis. The most important suggestions were that macroecologists and others should be testing the predictive ability of their hypotheses on new data sets: model fitting, in his opinion, is too often confused with model testing.